Friends and relatives of Sergio Adrian Hernandez Huereka, 15, stand over his coffin in his home before taking him away for burial in the northern border city of Ciudad Juarez, Mexico, Thursday June 10, 2010. A U.S. Border Patrol agent fatally shot Hernandez Monday after a group trying to illegally enter Texas threw rocks at officers near downtown El Paso, U.S. authorities said Tuesday.

EL PASO -- The U.S. government on Thursday launched a civil-rights investigation in the fatal shooting of a 15-year-old Mexican boy by a U.S. Border Patrol agent on the Rio Grande.

Sergio Adrían Hernández Güereca was shot and killed Monday by an agent trying to make an arrest during a rock-throwing incident near the Paso del Norte Bridge in Downtown El Paso.

U.S. Attorney General Eric Holder on Thursday described Hernández's death as "extremely regrettable" during a news conference about an unrelated drug operation in Washington, D.C.

Holder, according to a transcript provided by the Department of Justice, said the FBI is investigating the shooting of the Juárez teenager.

"The matter is under investigation," Holder said. "And we'll have to determine exactly what happened; who, if anyone, should be held responsible; what the circumstances were for the shooting. And all that is just a part of this ongoing investigation."

Federal officials confirmed that a civil-rights investigation was opened into the shooting of Hernández, who died on the Mexican side of the river from a bullet wound to the head.

Civil-rights investigations can look into crimes committed by law enforcement officers in the course of their duties.

In Mexico, the homicide investigation, which was being handled by Chihuahua state authorities, on Thursday turned into a federal case when it was taken over by the Mexico attorney general's office.

The shooting was recorded on a cell-phone video that was aired internationally on Wednesday by the Spanish-language Univision network.

The video shows an encounter that begins when a group of men try to cross a border fence near the railroad Black Bridge, just west of the Paso del Norte Bridge connecting Juárez to Downtown El Paso.

A Border Patrol agent is seen arriving on a bicycle, and rocks are allegedly being thrown at the agent while he tries to detain a man on the U.S. edge of the river. The agent is seen pointing his handgun. Three gunshots are heard.

Hernández can then be seen lying on the ground at the foot of the Black Bridge on the Mexican side of the mostly dry river. It is not shown if Hernandez was throwing rocks.

The teenager was buried Thursday in Juárez.

The boy's family described Her nández as a student who stayed out of trouble. But U.S. law enforcement officials said Hernández had a criminal record for sneaking undocumented immigrants across the border.

Mexican President Felipe Calderón on Thursday renewed his call for an "in-depth, impartial and objective" investigation into the recent deaths of two Mexican citizens by U.S. border agents.

Calderón referred to the deaths of Her nández and Anastasio Hernández-Rojas, 32, who died in the San Diego-Tijuana border area after officers struck him on May 28 with a stun gun and baton. The San Diego County medical examiner ruled that Hernández-Rojas' death was a homicide.

In a statement, Calderón said the teenager's case was especially serious because "Sergio Adrian Hernández was a minor, and he was killed by gunfire while on Mexican territory, in Ciudad Juárez."

"We are worried by the surge of violence against Mexicans, which is associated with the recent rise of anti-immigrant and anti-Mexican expressions in the United States," Calderón said.

Fernando Gomez Mont, Mexico's interior minister, in a statement on Thursday said he spoke with U.S. Homeland Security Secretary Janet Napolitano to express his concerns about the two deaths on the border.

Hernández's death appeared to be a few feet into Mexican territory.

The U.S. International Boundary and Water Commission, based in El Paso, is the official arbiter for boundary disputes along the border.

IBWC spokeswoman Sally Spener said it is easy to determine where the U.S. border begins and ends in the area where the shooting took place.

"The boundary is right down the middle of the channel," Spener said. "In fact, the Chamizal Project was created to avoid boundary disputes."

FBI officials and the video aired by Univision indicated that the Border Patrol agent, whom officials have not identified, was standing on the U.S. side of the border at the time of the shooting, and Hernández was on the Mexican side of the border.

Hernández's death sparked pro tests, a vigil and a fierce debate about whether the agent was justified in shooting. Immigrant-rights groups and Amnesty International condemned the shooting. Law enforcement groups said the agent had a right to defend himself because rocks were being hurled at him.

On Wednesday, the Border Patrol had extra agents in the area where the shooting occurred in case there was more trouble, but officials said Thursday that the number of agents was back to normal and things were quiet.

Daniel Borunda may be reached at dborunda@elpasotimes.com; 546-6102.

Diana Washington Valdez may be reached at dvaldez@elpasotimes.com; 546-6140.